2,4-D and 2,4-D butoxyethyl ester behavior in Eurasian and hybrid watermilfoil (Myriophyllum spp.).

BACKGROUND: Hybrid watermilfoil is becoming more prevalent in many lakes where the invasive Eurasian (Myriophyllum spicatum, EWM) and native northern watermilfoil (M. sibiricum) co-occur. These Eurasian and northern watermilfoil hybrids (HWM) grow 30% faster and in many cases are less sensitive to 2,4-dichlorophenoxy acetic acid (2,4-D) than either parent. The mechanism(s) impacting 2,4-D tolerance in these hybrids was investigated by comparing the absorption, translocation, metabolism, and desorption of two 2,4-D formulations in EWM and HWM. RESULTS: 2,4-D absorption in EWM and HWM was 5.7 and 7.9 times the external herbicide concentration determined by the plant concentration factor, a metric used to determine herbicide bioaccumulation, and 2,4-D butoxyethyl ester absorption was 35.6 and 52.1 times the external concentration in EWM and HWM, respectively. Herbicide bioaccumulation was greater in HWM than in EWM. Herbicide translocation to HWM roots was limited at 192 HAT and herbicide desorption in HWM was slightly lower than EWM. No differences were found in herbicide metabolism between the two plant species. CONCLUSION: 2,4-D resistance in HWM is not due to non-target-site resistance as no differences in herbicide absorption, translocation, desorption and/or metabolism were identified; therefore, target-site resistance is the most likely resistance mechanism. More research is needed to identify the molecular basis for the 2,4-D-resistant trait in HWM. © 2021 Society of Chemical Industry.

Endothall behavior in Myriophyllum spicatum and Hydrilla verticillata.

BACKGROUND: Endothall has been used to control submersed aquatic plants since 1960, providing broad-spectrum control of aquatic weeds. Although endothall is considered a contact herbicide, many field observations suggest that it might have systemic activity. The goals of this research were to determine endothall's (i) absorption characteristics, (ii) translocation from shoots to roots, and (iii) potential for desorption in Eurasian watermilfoil (EWM), monoecious and dioecious hydrilla. RESULTS: Endothall absorption was linear in dioecious hydrilla up to 192 HAT, while in EWM and monoecious hydrilla absorption data best fit an asymptotic rise function. Endothall absorption in EWM, monoecious and dioecious hydrilla was 3.3, 6.6, and 11.0 times the external herbicide concentration determined by the plant concentration factor. Translocation to EWM roots reached 7.9% of total absorbed radioactivity by 192 HAT, while translocation to monoecious and dioecious hydrilla roots reached 17.8% and 16.4% by 192 HAT, respectively. For all three species, no more than 30% of absorbed endothall moved from the plant to clean water 96 HAT. CONCLUSION: Endothall is a very water soluble compound and yet it accumulated in these three important aquatic weeds at concentrations significantly higher than the external herbicide concentration. These data provide evidence that endothall could have systemic activity in these aquatic species. Following 14 C-endothall applications, more 14 C translocated from shoots to roots compared to the translocation of 14 C for other systemic aquatic herbicides. The final confirmation of endothall's systemic behavior requires that the radioactivity found in the root system of these aquatic plants is 14 C endothall. © 2019 Society of Chemical Industry.